BP agreed to the settlement when it was first approved last year. But the firm has recently argued that rules approved by court-appointed claims administrator Patrick Juneau are allowing large businesses to be paid what could be billions of dollars for fictional losses. BP has said companies are receiving settlement payments based solely on how they choose to keep their business records, instead of for actual losses caused by the Deepwater Horizon accident and subsequent spill.

BP had originally estimated that the claims settlement would cost it $7.8 billion, but last month increased that estimate to $9.6 billion in a federal Securities and Exchange Commission filing, with a warning that the ultimate claims total could be even more.

In its new court motion, BP repeats arguments it made in its separate appeal of U.S. District Judge Carl Barbier's March 5 decision upholding how claims are paid. Barbier found that the Juneau was correctly interpreting provisions of the settlement between BP and private claimants that govern how claimants with large "Business Economic Losses" should be paid.

In that decision, Barbier said, "Objective formulas, the possibility of 'false positives,' and giving claimants flexibility to choose the most favorable time periods are all consequences BP accepted when it decided to buy peace through a global, class-wide resolution. In light of this, to the extent that the Claims Administrator's interpretation produces 'false positives' or, as BP claims, "absurd" results, it appears that the Settlement Agreement anticipates that such results would sometimes occur."

In its new challenge, BP argues that the rules are resulting in claims being paid for businesses that saw no losses. The oil giant pointed to a list of such claims it also used in its direct appeal of the rule, including $21 million to a Louisiana rice mill 40 miles from the coast that earned more in 2010, the year of the spill, than in any of the three previous years. The list also included a $3.3-million payment to a central Louisiana law firm whose profits exceeded its "benchmark" profits by 10 percent.

Those sorts of claims payments actually expand the class of people participating in the class action lawsuit, BP argued, and could discriminate against members of the class who suffered valid damages. As such, the company argued, if the appeals court upholds Barbier's interpretation, the settlement would violate a recent U.S. Supreme Court ruling that required lower courts to limit damage claims to victims.

"Given the misinterpretation, the settlement has been wrenched from reality and no longer resembles the deal to which we have agreed," said BP vice president Geoff Morrell. "The claims administrator's misinterpretation systematically pays claimants for inflated or wholly non-existent losses. It thus breaks faith with the core bargain reflected in the agreement -- namely, the compensation of claimants for actual lost profits."

But Steve Herman, a lead attorney with the Plaintiffs Steering Committee representing claimants, said BP's new challenge "makes clear that BP broke its promise to the Gulf."

In a statement, Herman said that, "When forced to actually be honest about its intentions, BP tells the court that it has no plans to stand by the transparent, objective agreement that it negotiated, signed, and asked the court to approve." The steering committee will file its own motion in the appeal later.

If its objections to the rules interpretation are upheld, the BP filing said, the settlement agreement should be upheld, despite the objections of fishers and Texas businesses and residents who contend they're inadequately covered by the settlement.